Rapid cooling device and method of rapidly cooling the device

ABSTRACT

A rapid cooling apparatus passing hot exhaust gas in a short time along a flow path formed in a cooling setting with piled up arrangement and having a reduced cross-sectional area of the flow path to reduce the volume thereof so as to cool rapidly to a temperature below a dioxin synthesizing temperature so that dioxins are prevented from generating, characterized in that multistage tube bodies for heat exchange to pass coolant therethrough are arranged in a rapid cooling cylindrical body for passing hot gas such as exhaust gas from an inlet opening to an outlet opening, and the cross-sectional area of the rapid cooling cylindrical body is being reduced gradually in a passing direction of the hot gas.

FIELD OF INVENTION

[0001] The present invention relates to a rapid cooling apparatus andits method capable of completely suppressing or preventing toxicsubstances discharged from, for example, various incinerators, meltingfurnaces and the like, from synthesizing dioxins secondarily.

RELATED ART

[0002] Cooling apparatuses employed in combustion equipment forincinerators, melting furnaces and the like are used not only in wastetreatments but also widely used in industries such as metal smeltingfacilities, pulp bleaching processes, cement plants, glass plants,ceramic plants, plants for manufacturing chemical material or productsand the like.

[0003] However, toxic dioxins are re-synthesized in cooled dischargedgas from the above-mentioned facilities and plants. Consequently, theatmosphere and the global environment have been being destructed so thatit has been being widely advocated that improvements on the global scaleare required.

[0004] For that purpose, various kinds of rapid cooling apparatuses havebeen developed so as to remove dioxins, which are air pollutants andtoxic.

[0005] Means to decompose dioxins by burning at high temperatures, meansto prevent synthesized dioxins from generating during cooling steps ofhot exhaust gas discharged to the atmosphere afterward, have been knownas apparatuses or methods for removing dioxins. However theseapparatuses or methods require complicated structures and cannotconstruct effective ones at low cost.

[0006] Organic substances and the like constituting synthetic resin suchas chlorine components, hydrogen components and the like are completelyreacted or decomposed into elements in the form of hot exhaust gas, whenthe substances are combusted in combustion equipment at temperatureshigher than 800° C. In these states, toxic dioxins are decomposed intonontoxic substances, but when the exhaust gas is cooled to a dioxinre-synthesizing temperature of ca. 340° C. an inconvenient problem thatdioxins are re-synthesized around this temperature, happens.

[0007] It was already proved through experiments and officially admittedby the Japanese government that hot exhaust gas should be rapidly cooledfrom 800° C. around which the exhaust gas is in a decomposed state, tobelow the dioxin re-synthesizing temperature of 340° C. within 16thousandths second in order to prevent dioxins from re-synthesizing fromdecomposed hot gas at a high temperature.

[0008] The present invention is carried out in view of theabove-mentioned fact in order to provide a more excellent rapid coolingapparatus and a method thereof capable of preventing dioxins fromre-synthesizing by modifying or developing previous inventions (Japanesepatent registered Nos. 3127249 and 3125217) invented by the presentinventor.

DISCLOSURE OF THE INVENTION

[0009] The present invention relates to a rapid cooling apparatusequipped with multistage heat exchanger tubes for passing throughcoolant, arranged in a rapid cooling cylindrical body for passing hotexhaust gas comprising chemical component molecules consisting ofdecomposed dioxins generated in various furnaces, from an inlet openingto an outlet opening of the cylindrical body. A cross-sectional area ofthe rapid cooling cylindrical body is gradually diminished in a passingdirection of the exhaust gas. The present invention also relates to arapid cooling method for exchanging heat between the above-mentioned hotexhaust gas and the coolant when the exhaust gas is passed at apredetermined flow velocity which is kept at an initial velocity withoutreducing the flow velocity by reducing the cross-sectional area of therapid cooling cylindrical body so as to keep up with reducing exhaustgas volume caused by dropping temperature of the exhaust gas and forcooling the exhaust gas down to a desired temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a cross-sectional view along I-I line in FIG. 2,illustrating a main arrangement of an embodiment of the rapid coolingapparatus by the present invention. FIG. 2 is a cross-sectional viewalong II-II line in FIG. 1. FIG. 3 is a cross-sectional view alongIII-III line in FIG. 1. FIG. 4 is a cross-sectional view along IV-IVline in FIG. 1. FIG. 5 is a longitudinal sectional view of a mainarrangement of another embodiment by the present invention. FIG. 6 is across-sectional view along VI-VI line in FIG. 7, illustrating a mainarrangement of other embodiment by the present invention. FIG. 7 is aplan view for explaining the arrangement in FIG. 6.

PREFERRED EMBODIMENTS BY THE PRESENT INVENTION

[0011] Embodiments are explained by referring to drawings for describingthe present invention in detail.

[0012] In this specification, “dioxins” include poly-chlorinateddibenzo-p-dioxins (hereinafter referred as PCDDs) comprising 75isomers/homologues and poly-chlorinated dibenzofurans (hereinafterreferred as PCDFs) comprising 135 isomers/homologues. Furtherpoly-chlorinated biphenyl (hereinafter referred as PCBs) comprising 209isomers/homologues include coplanar PCBs comprising 12isomers/homologues which show similar vital reactions to those of PCDDs.Since coplanar PCBs are also synthesized in waste incinerators andwidely pollute environments as PCDDs and PCDFs, coplanar PCBs are alsoincluded in and called “dioxins” altogether.

[0013] Structural formulas of these dioxins are shown below.

STRUCTURAL FORMULA OF DIOXINS

[0014] Hereinafter embodiments by the present invention are explained byreferring to drawings.

[0015] In drawings, a reference numeral “1” is a rapid cooling apparatushaving a rapid cooling cylindrical body 2, which shows a square orpreferably a rectangular shape in its plan view, a long rectangularlongitudinal shape in its side view and reducing its widths in its frontand rear views along a direction from the top to the bottom, and as awhole shows a cubic shape with compartment arrangements. A referencenumeral “3” represents an inlet opening formed on an upper side or alower side (in the drawings it is formed on the upper side) of the rapidcooling cylindrical body 2. The inlet opening 3 introduces hot exhaustgas with a temperature of more than 800°, comprising chemical componentmolecules of decomposed dioxins generated in various furnaces. Areference numeral “4” represents an outlet opening formed on the lowerside or the upper side (in the drawings it is formed on the lower side)of the rapid cooling cylindrical body 2 for discharging rapidly cooledexhaust gas, namely, cooled to lower than a so-called dioxinre-synthesizing temperature 300° C. for example, lower than 270° C.

[0016] In the rapid cooling cylindrical body 2, a tapered cylindricalperiphery t is formed such that cross sectional area of the cylindricalbody from the upper inlet opening 3 to the lower outlet opening 4reduces gradually as shown in FIG. 1 so as to squeeze a flow rate, inother words, flow volume of the introduced hot exhaust gas.

[0017] The tapered cylindrical periphery t can form on the rapid coolingcylindrical body 2 either with a rectangular or with a circular crosssection. It may be formed only on mutually facing inner surfaces. Italso may be formed around the whole periphery of the rapid coolingcylindrical body 2 such that the rapid cooling cylindrical body isformed in a pyramid or a cone.

[0018] A reference numeral “5” is cooling tubes for heat exchange,having a cross section of a preferable shape such as circular,rectangular or the like. Heat resistant metals such as stainless steel,titanium, zirconium and the like, and heat resistant ceramics areemployed for the cooling tubes piled one above the other such that aplurality of cooling tubes form multistage tube rows in the rapidcooling cylindrical body 2. Cooling air or cooling liquid is suppliedfrom one opening ends of the cooling tubes to the other opening ends.

[0019] Fins (not shown in drawings) for absorbing heat are arranged atrequired portions of the cooling tubes 5 and the cooling tubes 5 arearrayed on the same planes spaced apart by a predetermined distance eachother so as to form a planar cooling tube group “a” as shown in FIGS. 2,3 and 4. One planar cooling tube group “a” is piled above a neighboringplanar cooling tube group but is shifted a little against theneighboring planar cooling tube group such that a sectional view ofplanar cooling tube groups shows a checker pattern, where flow paths Fare formed from upper portion to lower portion of the rapid coolingcylindrical body 2.

[0020] There or four planar cooling groups a, a, . . . spaced apart by apredetermined distance, are put together so as to form a planar tubeblock. Coolant inlet openings 6 and outlet openings 7 of neighboringplaner tube blocks, arranged in a direction from the top to the bottomof the cylindrical body, are formed at opposite side each other as shownin FIGS. 3 and 4 so as to increase a cooling effect of the rapid coolingapparatus. The inlet openings 6 and outlet openings 7 are formedrespectively at two portions of one planar tube block as shown in thedrawings. And a spread room 6 a and a spread room 7 a are formedrespectively at an inlet side and an outlet side of each planar tubeblock comprising planar cooling groups a, a, . . . so as to keep coolantfrom spreading or accumulating effectively.

[0021] Reference numerals “8” and “9” are openings for attachingmeasuring devices (not shown in the drawings) to measure temperature ofexhaust gas at the upper and lower portions of the rapid coolingcylindrical body 2.

[0022] Hereinafter effects of the present invention are explained basedon the above-mentioned arrangements.

[0023] Effects when cooling air is employed as a coolant, are explainedhere.

[0024] Exhaust gas discharged from various furnace having a temperatureabove the decomposing temperature of the dioxins, for example, over 800°C.˜900° C. is introduced into the inlet opening 3 of the rapid coolingcylindrical body 2 of the rapid cooling apparatus 1 at a desired flowvelocity under a desired pressure.

[0025] Cold cooling air of an ordinary temperature is introduced viaright/left inlet openings 6 of each planar cooling block comprisingplanar cooling groups a, a, . . . and effectively exchanges heat withhot gas via walls of cooling tubes 5, and finally discharged from outletopenings 7 as warmed gas.

[0026] The hot exhaust gas is rapidly cooled at multistage planarcooling groups a, a, . . . , so that its temperature is lowered and itsvolume is also reduced as the hot exhaust gas is led through from theupper portion of the rapid cooling cylindrical body to the lowerportion.

[0027] Since the rapid cooling cylindrical body 2 is formed such thatthe tapered cylindrical periphery t is gradually decreased as in adirection from the inlet opening 3 to the outlet opening 4, a flowvelocity of the treated hot exhaust gas with reduced volume is keptalmost the same velocity without much varying from a flow velocity ofthe hot gas introduced from the inlet opening 3 of the rapid coolingcylindrical body 2. The exhaust gas is passed through the rapid coolingcylindrical body 2, and then discharged as cooled gas with a desiredtemperature from the outlet opening 4 formed at the lower portion of thecylindrical body.

[0028] In order to cool hot gas rapidly and effectively, the higher atemperature difference between the coolant and the hot gas is set, thebetter the cooling effect is. Therefore in the present embodiment, inletopenings of the cooling air are mutually arranged at opposite sides ofneighboring planar cooling blocks comprising planar cooling tube groupsa, a, . . . , so that temperature differences between the hot gas andcontact surfaces of cooling tubes 5 can set as high as possible, thusthe hot gas is rapidly cooled.

[0029] Particularly, when the hot gas is exhaust gas having componentswhich are re-synthesized into dioxins during a cooling stage, the hotgas should be cooled rapidly from a temperature higher than dioxindecomposing temperature, namely, 800° C.˜900° C. to a temperature lowerthan the dioxin re-synthesizing temperature, 300°, namely, 200° C.˜250°C. in a quite brief time less than 16 thousandths second.

[0030] When a temperature of introducing exhaust gas is set 900° C. anda temperature of discharged gas is lowered to 200° C. expanded rates ofhot gas at respective temperatures from a base temperature 0° C. atportions of the rapid cooling cylindrical body 2 from the top to thebottom are calculated as follows.

[0031] expanded rate at 900° C. (273+900)/273=4.296

[0032] expanded rate at 800° C. (273+800)/273=3.930

[0033] expanded rate at 700° C. (273+700)/273=3.564

[0034] and so on

[0035] n) expanded rate at 200° C. (273+200)/273=1.732

[0036] In conclusion, since hot exhaust gas is contracting its volume asits temperature is dropping, the tapered cylindrical periphery t may beformed around the rapid cooling cylindrical body 2 based on the abovecalculations.

[0037] When exhaust gas with its flow velocity of 20 m/sec is cooledfrom 900° C. to 200°, the following calculated result is obtained.

20 m/sec×{fraction (16/1000)} sec=0.32 m.

[0038] Namely, it is concluded that a passing distance of the exhaustgas corresponding to a height of the rapid cooling cylindrical body 2should be set 0.32 m=32 cm.

[0039] Hereinafter another embodied exhaust gas raid cooling apparatus1A by the present invention is explained by referring to FIG. 5.

[0040] In this embodiment, the tapered cylindrical periphery t of therapid cooling cylindrical body 2 of the previous embodiment is modifiedinto a step structure 1. A rapid cooling cylindrical body 2A is obtainedwhen the rapid cooling cylindrical body 2 is modified such that itscross sectional volume reduces stepwise in a direction from the top tothe bottom of the cylindrical body. As a result the exhaust gas can passthe cooling apparatus in a short time as a flow velocity being kept atthe initial value without reducing the flow velocity due to volumecontraction by heat exchange of the hot exhaust gas, in the same manneras the previous embodiment.

[0041] Since arrangement of cooling tubes 5, introducing and dischargingmethods of coolant and the like are same as the previous embodiment, thesame reference numerals are used and further explanation is omitted.

[0042] Further, other embodiment is explained by referring to FIGS. 6and 7.

[0043] This embodiment has the following different arrangements from thepreceding two embodiments. Hot exhaust gas is introduced and divide intoa plurality of flow tubes 12 longitudinally arranged by small spacingeach other in a rapid cooling cylindrical body 2B of a rapid coolingapparatus 1B. While cooling gas passes through multistage compartments10, 10 . . . from both sides of the rapid cooling cylindrical body 2B tothe opposite sides each other as shown by arrows in FIG. 6.

[0044] The arranged number of flow tubes 12 is being reduced graduallydownward so as to meet a volume nearly corresponding to contractedvolume of the exhaust gas. In other words as shown in the drawings, aflow path of the exhaust gas is reduced its width stepwise so that adischarging flow velocity of the exhaust gas is kept almost at the samevalue as an introducing velocity of the exhaust gas, thus the exhaustgas can be cooled to below the dioxin re-synthesizing temperature in abrief time, namely, within 16 thousandths second and can be discharged.

[0045] As materials for the flow tubes 12, preferably zirconium andtantalum are used in the uppermost stage (I) where the temperature ofthe exhaust gas is the highest, titanium is used in a middle stage (II)where the temperature is gradually dropped and Inconel alloy (JapaneseIndustrial Standard: SUS 316) is used in the lowermost stage, takingresistant and anticorrosion effects of the rapid cooling apparatus intoconsideration.

[0046] Since inlet opening and outlet openings of the exhaust gas of thepresent embodiment are the same as the preceding embodiments, the samereference characters are assigned. A reference numeral “11” is wallsdividing compartments 10, 10.

[0047] As described above, cooling air is used in these embodiments asthe coolant, liquid such as water and the like are also employedinstead.

[0048] Although not illustrated in the drawings, when exhaust gas whichcontains dioxins is at a relatively low temperature lower than 700°C.˜800° C. where dioxins are not completely decomposed, the exhaust gasshould be heated again so as to decompose dioxins completely, and whenmist is suspended in the exhaust gas, the exhaust gas should be passedthrough a high temperature multi-cyclone so as to remove the suspendedmist and keep its temperature over 800°. Then heated exhaust gas isintroduced to inlet openings 3 of the above-described rapid coolingcylindrical bodies 2, 2A and 2B.

POSSIBILITY OF INDUSTRIAL USE

[0049] Since the apparatus by the present invention can rapidly cool hotexhaust gas such as waste gas discharged from various furnaces, it canbe built in not only combustion equipment but also melting furnaces inplants. And it can be compactly and easily built in existing or newlyconstructing combustion systems, since it can suppress a quantity ofre-synthesized dioxins almost completely below 0.1 ng-TEQ/m³N, acriterion value of re-synthesized dioxins which said to be generated invarious incinerators used for waste treatment. The value is set forwaste incinerators with capacities more than 4 ton/hour by the Japanesegovernment.

[0050] Since the rapid cooling apparatus by the present invention has asimple arrangement, it can be used in various cooling apparatuses inaddition to the cooling apparatus for hot exhaust gas. Further, it issuited to construct at an inexpensive cost and to mass-produce.

1. A rapid cooling apparatus comprising a rapid cooling cylindrical body for passing hot exhaust gas from its inlet opening to its outlet opening and multistage heat exchange tubes for passing through coolant arranged in said rapid cooling cylindrical body, wherein: a cross sectional area of said rapid cooling cylindrical body is gradually reducing in a passing direction of said hot exhaust gas.
 2. The rapid cooling apparatus according to claim 1, wherein: the cross sectional area of said rapid cooling cylindrical body is reduced as smoothly as possible.
 3. The rapid cooling apparatus according to claim 1, wherein: the cross sectional area of said rapid cooling cylindrical body is reduced stepwise.
 4. A rapid cooling method for exchanging heat between hot exhaust gas and coolant via tubes when the hot exhaust gas passes at a desired flow velocity, wherein: a cross sectional area of a rapid cooling cylindrical body is adjusted to reduce in accordance with reducing volume of the exhaust gas as its temperature is dropping so as to keep an initial flow velocity without reducing and so as to cool the exhaust gas to a desired temperature.
 5. The rapid cooling method according to claim 4, wherein: said hot exhaust gas which includes dioxins discharged from a incinerator in a decomposed state, is cooled to below a dioxin re-synthesizing temperature within 16 thousandths second.
 6. A rapid cooling apparatus comprising a rapid cooling cylindrical body and flow tubes longitudinally arranged in said rapid cooling cylindrical body for dividing and passing hot exhaust gas and reduced in their number stepwise in a passing direction of the hot exhaust gas, wherein: coolant cooling paths for heat exchange are arranged in said rapid cooling cylindrical body so as to cool said flow tubes for hot exhaust gas on their sides.
 7. A rapid cooling method for exchanging heat by passing and dividing hot exhaust gas through a plurality of flow tubes arranged in a rapid cooling cylindrical body so as to cross a flow direction of the coolant, wherein: the number of said plurality of flow tubes is reduced in a flow direction of the exhaust gas so as to keep a flow velocity of heat exchanged and cooled exhaust gas at almost same as a flow velocity of an inlet side.
 8. The rapid cooling method according to claim 7, wherein: said hot gas which includes dioxins discharged from an incinerator in a decomposed state, is cooled to below a dioxin re-synthesizing temperature within 16 thousandths second. 